This invention generally pertains to voltage regulators, and more particularly AC voltage regulators able to provide a desired AC voltage to any type of a given load, without any output power interruptions during any regulation period and without distortion of the AC sine wave. The benefits associated with the use of the present invention include reduced size and cost of the voltage regulating devices, reduced electrical energy consumption and increased equipment life in electrical installations.
A voltage regulator is designed to deliver and automatically maintain a constant voltage level to a load. If the incoming voltage is too high or too low compared to a desired predetermined range, the voltage regulator will reduce or increase the voltage so that the output voltage falls within the range. Such voltage regulators are used to provide a steady voltage level to a load independent of variations in the voltage transmitted from the power source, which can cause the voltage to fall above or below the desired output. This is especially important to sensitive electrical devices that may become damaged if the voltage is not maintained properly. Additionally, voltage regulators can be used as energy saving devices by stably delivering a lower range of voltage to a load that still falls within the operational voltage range.
Voltage regulators often utilize transformers or autotransformers with multiple taps to adjust the voltage. Voltage regulators also typically use a number of high frequency switches and relays to direct the current passing through the device in order to maintain the voltage, or to step-up or step-down the voltage. Problems arise when the device switches from one mode of operation to another mode (for example, switching from normal mode to a step-up mode) momentarily disconnecting the power source from the load or producing transient currents that electrically saturate part of the circuit. This can cause momentary power interruptions or overload parts of the circuit causing damage to the device.
Several patents have tried to overcome these deficiencies. U.S. Pat. No. 5,545,971, U.S. Pat. No. 6,020,726, and U.S. Pat. No. 6,046,549, for example, disclose voltage regulators utilizing a single regulator transformer having a primary winding and a secondary winding. Further, a relay or plurality of high frequency AC switches are included so as to variably set a plurality of connection modes to maintain either step-up, step-down modes or a short-circuit mode where voltage passes through the secondary winding of the transformer with the primary winding being completely isolated from the secondary winding. With higher power, the circuit will face typical disadvantages such as oversaturation without appreciable voltage regulation during the switching transient, wave form distortion and questionable dependability. None of these devices disclose a means for preventing electrical overloads or power interruptions during the brief periods when the switches or relays switch from one configuration to another. Thus, it is unlikely these systems can be widely used with industrial systems.
What is needed is a high efficiency voltage regulator suitable for use with both high and low rated power that is also able to switch between different modes of operation without damage to the device or loss of power. It is preferable that such a device provide regulated voltage for AC power without a distorted waveform output. The purpose of the present invention is to provide an improved power switching circuit and a voltage regulator containing such a power switching circuit.